In an internal combustion engine, the structure of which is such that an explosion of fuel occurs at a top dead point of a piston in a bore and the piston is pushed down by the explosion, temperature rises on an upper side of a cylinder bore wall and temperature falls on a lower side of the cylinder bore wall. Therefore, a difference occurs in a thermal deformation amount between the upper side and the lower side of the cylinder bore wall. Expansion is large on the upper side and, on the other hand, expansion is small on the lower side.
As a result, frictional resistance between the piston and the cylinder bore wall increases. This causes a decrease in fuel efficiency. Therefore, there is a need to reduce the difference in the thermal deformation amount between the upper side and the lower side of the cylinder bore wall.
Therefore, conventionally, in order to uniformize a wall temperature of the cylinder bore wall, it has been attempted to set a spacer in the groove-like cooling water channel for adjusting a water flow of cooling water in the groove-like cooling water channel and controlling cooling efficiency on the upper side and cooling efficiency on the lower side of the cylinder bore wall by the cooling water. For example, Patent Literature 1 discloses a heat medium channel partitioning member for internal combustion engine cooling including: a channel partitioning member disposed in a groove-like heat medium channel for cooling formed in a cylinder block of an internal combustion engine to partition the groove-like heat medium channel for cooling into a plurality of channels, the channel partitioning member being formed at height smaller than the depth of the groove-like heat medium channel for cooling and functioning as a wall section that divides the groove-like heat medium channel for cooling into a bore side channel and a counter-bore side channel; and a flexible rip member formed from the channel partitioning member toward an opening section direction of the groove-like heat medium channel for cooling and formed of a flexible material in a form with a distal end edge portion passing over one inner surface of the groove-like heat medium channel for cooling, whereby, after completion of insertion into the groove-like heat medium channel for cooling, the distal end edge portion comes into contact with the inner wall in an intermediate position in a depth direction of the groove-like heat medium channel for cooling with a deflection restoration force of the distal end edge portion to separate the bore side channel and the counter-bore side channel.